Hot Topics [Top]

Topics [1][2][3][4][5][6][7][8][9][A][B][C][D][E][F][G][H]

Cold topics 1 (Band Map in Japan, 4/24, 1997)

The author makes the Band (calculation) Map in Japn.
[Band map in Japan]

Cold topics 2 (BEST 10)

The author selects the best 10 papers for electronic structure calculations.
[Best 10]

Hot topics 3 (TMC, TMN surfaces)

At 1996, the author started the study of the TiC(001)-1x1 surface system by using the first-principles molecular dynamics (FPMD) method. Already, this have been calculated by some theoretical groups(Ref: D. L. Price, J. M Wills and B. R. Cooper(PWC), Phys. Rev. Lett., Vol77, No.10, p3375(1996), some other references there in.). In addition, ZrC, NbC, HfC and TaC(001)-1x1 surfaces have also been studied [1]. Electronic and lattice properties of bulk for NbC, HfC, ZrC, OsC and TaC are caluclated at a NaCl structure with and without PCC(See [table IV],png,5.4KB) in order to investigate which atom(carbon or transition metal[TM]) is outward or inward on the surface(6/24, 1998). The accuracy with pcc is slightly better than that without pcc(4/14, 1999) for bulk.
The (001) surface is non-polarized in which the numbers of carbon and TM atoms are equal each other on the outermost layer. In this study, the transition metal (TM) carbide surface (periodic super cell model including 9 TM-C layers as a slab and vaccum region as the same thickness of slab) are optimized only in a [001] direction. The surface electronic structures in the optimized structures are metallic in all cases. (Bulk TiC[rock salt structure] is also metalic.) In most cases, the carbon atoms are displaceed outward and TM atoms inward on the top layer with and without PCC, except for the case of TiC without PCC. This trend for TiC and TaC agrees with above theoretical results(PWC). Moreover, charge densities of surfaces, work function, etc. are calculated in this study(4/25, 2000). As for TM pseudopotentials, it is found that considering a partial core correction(PCC, S. G. Louie, S. Froyen and M. L. Cohen, Phys. Rev. B26, 1738(1982)) is very important in the structural optimization.

Transition metal nitride surfaces (TiN, ZrN, NbN, HfN and TaN(001)-1x1) have also been investigated [2].

Reference:
[1] K. Kobayashi: Jpn. J. Appl. Phys. Vol. 39, No. 7B (2000) 4311.
[2] K. Kobayashi: Surface Science 493 (2001) 665.: (for TMN surfaces, [DOI: 10.1016/S0039-6028(01)01280-8](*))
[3] K. Kobayashi, "First-principles study of the TiX(X = B, C, O, N and F) surfaces", in proceedings of JK2000, (2001) 285. [PDF](nims.go.jp/cmsc/, PDF, 174 kb)
[4]K. Kobayashi, N. Kobayashi, and K. Hirose, "First-Principles Study of TiN/MgO Interfaces", e-J. Surf. Sci. Nanotech., 12 (2014) 230 - 237 (ACSIN-12 & ICSPM21) [DOI: 10.1380/ejssnt.2014.230]
[5]K. Kobayashi, H. Takaki, N. Kobayashi, and K. Hirose, "Electronic Band Structure of Various TiN/MgO Superlattices", JPS Conf. Proc. 5 (2015) 011013 (CSW2014).
[6]Hirokazu Takaki, Kazuaki Kobayashi, Masato Shimono, Nobuhiko Kobayashi and Kenji Hirose, "First-principles calculations of thermoelectric properties of TiN/MgO superlattices - the route for enhancement of thermoelectric effects in artificial nanostructures", J. Appl. Phys. 119 (2016) 014302.

[Figure](png,30KB,TiC(001)1x1 surface [structural optimized], Green and red circles are C and Ti, respectively.)

Cold topics 4 (Ga, High pressure)

The author attempts to investigate electronic band structures in a variety of pressure conditions[from 3 to 300 GPa] for Ga(fcc) and In(fcc). In this calculation, shallow 3d and 4d core states are treated as valence states in order to obtain critical pressures of overlapping of 3d and 4s (4d and 5s) states for Ga (In).
It is found that the critical pressures are about 70GPa for Ga and 120GPa for In[1](Japanese version),[2](Abstract,large postscript file , 160kbytes),(Proceedings of AIRAPT-16 and HPCJ-38, Vol. 7, 196-198(1998),Very Large postscript file,623kb), K. Takemura, K. Kobayashi and M. Arai, Phys. Rev. B58, 2482-2486(1999) for Ga only. As a result of theoretical calculations, a contribution to critical pressure of phase transition(bct-fcc) for Ga due to overlapping of valence s and shallow core d states is small(4/14, 1999).
On the other hand, it should be noted that the actual shallow d core states for Ga and In are deeper than those calculated on the basis of the local density approximation(LDA) in the density functional theory[refer to E. Wigner, Phys. Rev. 46, 1002(1934), W. Kohn and L. J. Sham, Phys Rev. 140, A1133(1965), P. Hohenberg and W. Kohn, Phys. Rev. 136, B864(1964)].
Recently(1/20, 1998), the author have studied to calculate electronic properties of Tl under high-pressure conditions. The critical pressure of overlap between valence 6s- and core 5d-states for Tl is 10 GPa because of a very shallow core d-state. This figure(png file, 20KB) is a variation of electronic band structures of Tl from 1 to 128 GPa.
These critical pressures may be underestimated on the comparison with the actual critical pressures in which the bottom of the valence states touches the top of the shallow core states, respctively. This suggests that it is necessary to consider beyond LDA calculation(GGA,SIC,GW-approximation,etc.).

Cold topics 5

(Update 6/28,1996) [Legendre(l=3)] (png,large,about 30KB)

Cold topics 6 (Important Papers)

The author selects the important papers for electronic structure calculations.
[Important papers]

Cold topics 7 (Memorandum)

The author selects the memorandum for electronic structure calculations.
[Memorandom]

Cold topics 8 (Materials)

The author selects papers of materials by using the electronic structure calculations.
[Materials]

Cold topics 9 (Info. DFT,LDA)

The author selects papers of DFT,LDA and related topics.
[DFT,LDA]

Hot topics A (Main site and BandStructure.jp)

The author's main and "BandStructure.jp" sites have been opened.
Main [site]
BandStructure.jp [site]

Cold topics B (MgB2)

We calculate the MgB2(AlB2 structure: P6/mmm) bulk systems under various compression conditions (hydrostatic, c-axis[1] and a,b-axis[2]).
Electronic and lattice properties are obtained by using the FPMD. In detail, please see references[1][2][3].
[1] K. Kobayashi and K. Yamamoto, J. Phys. Soc. Jpn., Vol. 70, No. 7 (2001) 1861.
[2] K. Kobayashi and K. Yamamoto, J. Phys. Soc. Jpn, Vol. 71, No. 2 (2002) 397.
[3] K. Kobayashi, M. Arai and K. Yamamoto, J. Phys. Soc. Jpn. 72, No. 11 (2003) 2886.

Hot topics C (LiBC)

We calculate the LiBC(hexagonal, A-B stacking: P63/mmc symmetry) bulk systems under various compression conditions (hydrostatic, c-axis and a,b-axis)[1][2]. Electronic and lattice properties are obtained by using the FPMD and all-electron method(FLAPW: WIEN2k code for LiBC).

We found the lattice anomalies of LiBC and HBC under anisotropic compression (a, b-axis compression). Lattice constants c for LiBC and HBC contract under a, b-axis compression. Lattice constant a (b) of MgB(h-BN) contracts under c-axis compression. These anomalous behaviors show a kind of negative Poisson ratios. HBC and MgB(h-BN) are hypothetical compounds.

In detail, please see references[1]-[6].
[1] K. Kobayashi and M. Arai, "LiBC and related compounds under high pressure", Physica C 388 - 389 (2003) 201 - 202 (LT23).
[2] K. Kobayashi and M. Arai, "Lattice Anomaly of LiBC and Related Compounds under Anisotropic Compression", Journal of the Physical Society of Japan, Vol. 72, No. 2 (2003) 217.
[3] Related paper: K. Kobayashi, M. Arai and K. Yamamoto, J. Phys. Soc. Jpn. 72, No. 11 (2003) 2886.
[4] K. Kobayashi and M. Arai, Mater. Trans., Vol. 45, No. 5, (2004) 1465 - 1468.
[5] K. Kobayashi and M. Arai, Molecular Simulation, Vol. 30, No. 13 -15 (2004) 981 - 986 [ICMS-CSW2004].
[6] K. Kobayashi, M. Arai and T. Sasaki, "Lattice Anomalies of MBC (M = H, Li, Na) Under Anisotropic Compression", , Trans. MRS-J, Vol. 29, No. 8, 3799 - 3802 (2004) [IUMRS-ICAM2003].:(Related paper)

Hot topics D (BC-compounds)

We calculate a hypothetical hexagonal layered compound of C6B2 and related materials in order to search new superconductors.
Some of them have characteristic unoccupied flat bands close to the Fermi level at the Γ - A line. One of them[1] shows weak anharmonicity for a B-C bonding. Most of calculated compounds are energetically unfavorable. More detailed lattice dynamics calculations and to search more stable structures are our next task.

In detail, please see references[1]-[3].
[1]K. Kobayashi, Y. Zenitani and J. Akimitsu, "First-Principles Study of C6B2", Physica C, Vol. 426-431, Part 1. (2005) 374 - 380 [ISS2004] <-- As a result of more accurate calculations, we find that anharmonicity of C6B2 is weak (b4/(a2)2 is about 1).
[2]K. Kobayashi, M. Arai and K. Yamamoto, "First-principles study of C6B2 and related compounds", in proceedings of IWSDRM2005 (STAM, Vol. 7, Supplement 1 (2006) 71 - 77).
[3]K. Kobayashi, M. Arai and K. Yamamoto, "First-principles study of C6M2 (M = B, Al, Mg, Li), C7B and related compounds", Mater. Trans., Vol. 47, No. 11 (2006) 2629 - 2637[AlC2, MgC2, LiC2, LiB2].
Related [page](B-, C- and BC-compounds, go to bandstructure.jp)

Hot topics E (h-BN)

We calculate various hexagonal BN phases in order to investigate their electronic (electronic band structures, direct or indirect band gap, VBM - CBM) and lattice properties.
VBM: Valence band maximum CBM: Conduction band minimum

The electronic band structure of [h-BN](png, 26.2 KB, bandstructure.jp).

In detail, please see the reference[1].
[1]K. Kobayashi, K. Watanabe and T. Taniguchi, "First-principles study of various h-BN phases", Journal of the Physical Society of Japan, Vol. 76, No. 10 (2007) 104707.

Hot topics F (5H-BN)

We calculate 5H-BN and related polytypes in order to investigate their electronic and lattice properties.
The electronic band structure of [5H-BN](png, 40 KB, bandstructure.jp).

In detail, please see the reference[1].
[1]K. Kobayashi and S. Komatsu, "First-principles study of 5H-BN", Journal of the Physical Society of Japan, Vol. 76, No. 11 (2007) 113707.

Hot topics G (BN)

We calculate 2H, 3H(=3C), 4H, 5H and 6H polytypes for BN, SiC and AlN in order to investigate their electronic and lattice properties.

6H polytype has two crystal structures as ABCACB and ABCBCB. Crystal symmetries of ABCACB and ABCBCB are P63mc and P3m1, respectively. A stacking sequence of ABCACB is most commonly accepted. Total energies of 6H-BN(ABCACB) and 6H-SiC(ABCACB) are lower than those of 6H-BN(ABCBCB) and 6H-SiC(ABCBCB). In contrast, the total energy of 6H-AlN(ABCBCB) is lower than that of 6H-AlN(ABCACB). The total energies of BN and AlN polytypes are related to their hexagonalities.

In addition, we have investigate 10H-BN and 10H-AlN[2]. The 10H polytype has 58 structures. We choose four polytype structures whose hexagonalities (H) are 20, 40, 60 and 80 %. The total energy of the calculated 10H-BN structure increases with increasing hexagonality and that of the calculated 10H-AlN structure decreases with increasing hexagonality. This trend is consistent with the previous study of 2H - 6H polytypes for BN and AlN[1]. The band gaps of the calculated 10H-BN and 10H-AlN polytype structures are indirect.

Furthermore, we have calculated 8H-, 10H, 12H- and 18H-SiC polytypes[5]. In this study, it is found that 10H-SiC(ABCACBCACB, H = 40 %, Zhdanov notation: 3322)) is most stable in the calculated SiC polytypes[1][5]. This trend is invariant in LDA[BH] and GGA[PBE] calculations.

In detail, please see the reference[1].
[1]K. Kobayashi and S. Komatsu, "First-principles study of BN, SiC, and AlN polytypes", Journal of the Physical Society of Japan, Vol. 77, No. 8 (2008) 084703.
[2]K. Kobayashi and S. Komatsu, "First-principles study of 10H-BN and 10H-AlN", Journal of the Physical Society of Japan, Vol. 78, No. 4 (2009) 044706.
[3]K. Kobayashi and S. Komatsu, "First-Principles Study of 6H-AlN under various pressure conditions", J. Phys.: Conf. Ser. 215, 012111(2010).
[4]K. Kobayashi and S. Komatsu: "First-Principles Study of 30H-BN polytypes", Materials Transactions, Vol. 51, No. 9 (2010) 1497[6H-BN, 30H-BN].
[5]K. Kobayashi and S. Komatsu, "First-Principles Study of 8H-, 10H-, 12H-, and 18H-SiC Polytypes", Journal of the Physical Society of Japan, Vol. 81, No. 2 (2012) 024714[8H-SiC][10H-SiC][12H-SiC][18H-SiC].
[6]K. Kobayashi and S. Komatsu, "First-Principles Study of Various BN, SiC, and AlN polytypes", Trans. MRS-J, Vol. 37, 583-588 (2012)[IUMRS-ICEM2012][20H-SiC][30H-AlN][48H-BN].
[7]K. Kobayashi and S. Komatsu, "First-Principles Study of AlBN and Related Polytypes", Trans. MRS-J, Vol. 38[3], 485-492 (2013)[4H-AlBN][4H-AlAsN][4H-AlPN][2H-, 3H-, 5H-, 6H-, and 12H-AlBN][3x2H-AlBN].

Reprints of [10H-SiC][30H-BN][10H-BN(10H-AlN)][6H-AlN][5H-BN][h-BN] are availabe at present. We can send the reprints by request (E-mail).

(References)
[BH] U. von Barth and L. Hedin, J. Phys. C5, 1629(1972).
[PBE] J. P. Perdew, K. Burke, and M. Ernzerhof, Phys. Rev. Lett. 77, 3865(1996).

Hot topics H

We have calculated the TiN/MgO interfaces.

Please see the references [4][5][6].

Hot topics I

In preparation.

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